President Vladimir Putin could show up at the event, to take place in the capital's main sports stadium eleven days before the December 2 parliamentary elections, Pavel Astakhov said.
"We fixed the final date for a forum of Putin's supporters today. It will take place on November 21 at Luzhniki," said Astakhov, a famous lawyer and co-chairman of the Russian For Putin Movement, which publicly asked the president earlier in November to run in the March 2008 presidential polls despite a constitutional prohibition on a third consecutive term.
Astakhov said the forum was being organized by the ruling United Russia party, which is widely expected to win an overwhelming majority of seats in the State Duma. Putin, who tops the party's election list, has been accused by the opposition of using administrative resources to promote the party.
"We will hold it along with United Russia. There is nothing strange in this, as they share our views," Astakhov said, who stressed that his movement comprises people who are not members of the ruling party.
He did not give details of the forum's agenda, but said an invitation had been sent to Putin.
Astakhov said the movement has sought to ensure the continuity of Putin's foreign and domestic policies "in the transitional period" of parliamentary and presidential polls, by exercising control over lawmakers.
Analysts say that as well as urging the president to run for a third term, the movement For Putin could propose, on behalf of the nation, a new power setup with a new role for Putin as "national leader" after the presidential polls.
Movement activists have held meetings to support Putin since late October. Astakhov earlier said in a newspaper interview that amending the Constitution to allow Putin to stay in power was not impossible: "Any law is a living organism that is subject to change if the nation wants it. The job of lawmakers is to draft relevant mechanisms."
Putin, credited in Russia for bringing stability, presiding over strong economic growth, and strengthening the country's global role, has repeatedly rejected supporters' proposals to run for a third term and to amend the Constitution to this end.
However, political commentators continue to discuss possible loopholes that would allow Putin to run for president again without violating the Constitution, or to find a new role as de facto national leader.